The UK's highest court has ruled Boris Johnson broke the law by deciding to suspend Parliament for five weeks.
The Supreme Court in London says there was "no justification" for the shutdown.
House of Commons speaker John Bercow says Parliament should now be recalled "without delay".
President of the Supreme Court, Lady Hale said the decision was unanimous.
The implications of this ruling for Brexit and Ireland remains unclear, but Mayo deputy Lisa Chambers, the Fianna Fail spokesperson on Brexit, says it will certainly put the British Prime Minister under pressure to resign.
She says that may result in an extension to the Brexit date, but it will not solve the problem of getting a Brexit deal that works for Ireland.